std::size

Defined in header <iterator>

template < class C >
constexpr auto size( const C& c ) -> decltype(c.size());

(1)

(since C++17)

template < class T, size_t N >
constexpr size_t size( const T (&array)[N] ) noexcept;

(2)

(since C++17)

Returns the size of the given container c or array array.

1) Returns c.size().

2) Returns N.

Parameters

c	-	a container with a `size` method
array	-	an array of arbitrary type

Return value

The size of c or array.

Exceptions

noexcept specification:

noexcept

Notes

In addition to being included in <iterator>, std::size is guaranteed to become available if any of the following headers are included: <array>, <deque>, <forward_list>, <list>, <map>, <regex>, <set>, <string>, <unordered_map>, <unordered_set>, and <vector>.

Possible implementation

First version

template <class C> 
constexpr auto size(const C& c) -> decltype(c.size())
{
    return c.size();
}

Second version

template <class T, std::size_t N>
constexpr std::size_t size(const T (&array)[N]) noexcept
{
    return N;
}

Example

#include <iostream>
#include <vector>
#include <iterator>
  
int main() 
{
    std::vector<int> v = { 3, 1, 4 };
    std::cout << std::size(v) << '\n'; 
  
    int a[] = { -5, 10, 15 };
    std::cout << std::size(a) << '\n';
}

Output:

3
3

Links:

http://en.cppreference.com/w/cpp/iterator/size

doc_CPP

2025-01-10 15:47:30

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